Tuning indicator for frequency shift telegraphy



B. A. TREVOR 2,613,271

TUNING INDICATOR FOR FREQUENCY SHIFT TELEGRAPHY Filed April '7, 1950 5 n a x 2% Z 5 I .Z 0 H I. 7 2. a 1 M 5 5 9 .T 7 A 1 E Z i s E ym K e 2 E F. 00 E E /C 7M0 W N. W M J h F 5 F M-mzi) s-r/zzfz) Y FEEQ- INVENTOR bezgmmlzpvor A ORNEY Patented Oct. 7, 1952 TUNING INDICATOR FOR; FREQUENCY SHIFT TELEGRAPHY Bertram A. Trev0r,;Riverhead, N. ;Y. assignor to q f f America, a corporation Radio Corporation 0 ofiDelaware.

' Applicaticn'Aprili, 1950, Serial No. 154,"650. I

:1: I This invention relates o-avisual =tuning.. indicator for frequency shift FS) telegraph receivers. More particularly, itrelatesto azcathode ray tube turning indicator circuit tonsuch receivers. a L

Some FS receivers have separate mark and space filters for detection. An example of a three-set diversity receiver of this type is disclosed in my copending-application, Serial-No. 106,455, filed July 23, 1949.= Such adiversity receiver has separate mark and space filters. in each of thethree-diversifiedchannels. In :this type of receiver; it is desirable to have the markspace filter crossover frequency accurately centered between the received mark-space frequencies. Such adjustment allows reception of signals having rather large ranges ofirequency shift Without the possibility-of-one :otrthe. frequencies falling outside of one oi the-filter.passbands. In FS telegraphy; as is known to those skilled in the art, two frequencies are. alter natively present'at the receiver. Attheltransmitter these frequencies are keyed, onefrequency representing mark-and the otheryspace.

For visual display-purposes, the. circuit .of this invention utilizes a cathode ray tube. A-ncbject of this invention is to devise-an indicator .circuit wherein the cathode-ray tube may be changed without affecting the calibration iof the. system. This is truein spite-of the fact that-a large-.difierence in sensitivity may exist between tubes;

Another object is "to provide an indicatorcircuit which will'give avery accurate :indication of the tuning of an FS telegraph..receiver.

The ioregoingand'other objects .ofztheimvention will be best understood "froinmthe uiollowing description of some examples thereof, reference being had to the accompanying: drawinn'nwhere- Fig. 1 is a diagrammatic representation: oizan indicator circuit accordingisto this r-inventlom;

to supply a. large voltage.Ltoxone'svertical deflecting plate and a small woltagepto gonechorizontal deflecting plate. This:willproduce awslant line on the face of the tube. The amplified output of thespace filter. is'connectedytosupply a large voltage to the other vertical deflecting plate lzefllai-ms. (01. 173.49

Fig. 2 is a set'of characteristics:xmeiuluinyexr plaining the invention; and

space detector.

islowerthan the receive n1 n dea h shipoten e .nected-toone; of gthe yertica dc cting rplate slfw r-a a ode. av u edssi na s ew by and a. small voltage 130 said :onelhorizcntal dc flectingplate; .ThisWill :produce a line slanted in the opposite direction. With .telegrajphrkey- -ing; mark and =,space, signals are alternatively :present. .displayingan .Xi" on the tubes. face.

With correct tuning, a symmetrical marrow: fXf

results. .A-rrequency displacement in one. direction causes one -.leg-;.cf the to increaseiand .thcother :toldecrease in length. .A frequency displacement in the other. direction reverses; the

action. i

.Now referring. to Fig. 1, .a mark filter {I anda spacefilter .2 :are connected inparall'el to a pair of input terminals .:3: and l. Terminal; .4.;;is :g'rounded. To ;thej.t,erminals...3 and 4 is: supplied .ES' keyed .energyrxfrom: the intermediate ire: -quency. stage .of .,-.an' .FS .:receiver.

However, if desired, :the energysupplied to such terminals may :be. .in the audio .range. For. example; the space frequency maybe:2975-cycles1and the mark frequency .2125 cycles; To effect this result, :the

signal may .bexheterodyned. down to .the audio range. It will-.bezappreoiated:thatthese discrete .mark: and spaceirequencies are alternatively present at terminalswtrand i and are keyedqto represent intelligence. i

. One output lead iof eachofzthefilters [and "isgrounded. The ungrounded flead [of filter; J. is

connected at 51to-a1 mark detector and. the ungrounded lead of filter 2 is connected atzfitfl a The output; of ,mark filter l isfed to mark amplifier tube l;. by m. ans..0f .a co ne t nio "the ungrounded loutputhlead'oi such filter'to control gridsB ofctube l; Thecathod 9 -of tube 1 is grounded through resistor [.0 andxpotenltiometric resistor .l l the movablegtap' on which is connected :to; ground. A markresonan cirthis waath m r wam li fi b iv t mark resonant circuit IZ and may thus besconsldered, to ether with; mar sfil e 1 I .3 s pr app yin -a signals; of 'mark i ec enc toteslective means 1,2. 1.;Whenthe received; markfire: qu c is 1 5 c l cth a rewnen f s W 19 ci .1 a b l9 0;; c s-; 1 nvse e allwtl e reson nt fr qu nc the reso a cir ui numeral. One side of the resonant circuit The connections. just mentioned .are .for signal utilization .purposesnso. that the .intelligencemaybe madeauseoi. i a

'Line' B isslanted in an line A,'pro'duced by the marks'ignah -Wi'th=te1enected together through a resistor 20, of 1 n ce:- h

ohm for example.

Due to the connections of the voltage dividing network so far described, a mark-frequency Sig- .nal will pass through filter I, be amplified in],

will pass through circuit 12 and will supply a ,acteristic of space filter 2). resonant circuit l2 may be termed a first selecaiaaii output of the mar-i: resonant circuit I2 is quite high in the vicinity of the mark frequency (which is below the frequency of the crossover point Y and is approximately in the center of and is approximately in the center of the hori- I zontal portion of the frequency response char- Therefore, mark tive means for passing signals of mark frequencyand attenuating signals of space frelarge voltage to vertical deflecting plate 13 andv a small voltage to horizontal deflecting plate 18. This will produce a slant line A on the face of the cathode ray tube.

I 'he'output'of space filter 2 is fed to space amplifier-tube 2| by means ofa connection of the ungrounded outputlead of such filterto control grid 22 of tube; The cathode 23 of tube 2| is grounded through resistor 24 and potentiometric resistor I I, opposite ends of which are connected to cathodes 9 and 23.- A space resonant circuit 25, consistingoi an inductance, capacitance and resistance in parallel, is connected to the anode or output circuit of amplifier tube 2|. In'this way, the space amplifier tube 2| drives the space resonant circuit 25 and may thus be considered, together with space fllter 2, as means for-applying signals' of space frequency tothe selective means 25. When the received. space frequency is v2975 cycles, the resonant frequency of. circuit 25 maybe 3200 cycles. In general, the resonantfre- 'quency of the space resonant circuit is higher than the received space frequency.v The anode or highpotential side'of circuit25 is connected to the other vertical deflecting plate 26 of cathode ray tube l4. One side ofthe resonantcircuit 25 is connected to theanodev 21 of tube2l.

The opposite low potentialfiside of'circuit 25 is connected'to the horizontal deflecting plate I6 of tube l4 and to positive supply 11.

Vertical deflecting plate 26 is connected to horizontal defiecting'plate I8 through a resistor '28 0f rather high'resistance, for'example .3.3

megohmsw q I Du'e to the connections-of thevoltagedividing I network just described, a space fr'equency signal will pass through filter 2, be amplified in 2.l,.will pass throughcircuit25 and will supply alarge voltage to vertical deflecting plate26 and' a-smal1 voltage to horizontal deflecting plate" l8. This will produce a slantdine B on the faceofthe cathode ray tube; I f I opposite direction to graph keying,- mark and spac'e signals -are noron; the cathode ray tube face;

mark' an'd space resonant circuits l2 and 25".; 'Ih'e legends fo'rthe curves "'denote the components *to which the respective curves apply.-

will be observed that, starting from' a lowfrequency and moving upward, theoutput of the mark 'resonant circuit--12 increases as the frequency --a proaches there'sonant peak and decrea'sesas the frequency approaches that of -the filter crossover point Y, *It maybe-note ally alternatively present, displaying anf-X q'uency; -In-a; similar manner, starting from a' high frequencyand moving downward, the output of the'space resonant circuit 25 increases toward resonance and decreases toward the crossover frequency Y. It may be noted, from Fig. 2, that the output of the space resonant circuit 25 isquite highin the vicinity of the space frequency (approximately in the center of the characteristic of space filter 2), and is quite low in the vicinity of the mark frequency (approximately in the center of the characteristic of markfllter l). Therefore, space resonant circuit 25 may be termed a second selective means for passing signals of space frequency and attenuating signals of mark frequency.

The characteristics of the mark and space resonant circuits !2 and 25 are similar. Therefore, when the mark and space frequencies received are equally disposed about the filter crossover frequency Y, equal voltages appear at the outputs of resonant circuits l2 and 25, making the two lines A-and B on the face of the tube of equal length. Thus, under these conditions a symmetrical X is displayed on the face of thecathode ray tube.

If, now, the mean of the received mark and space frequencies shifts below the frequency Y, the output of resonant circuit [2 will increase (assuming that the mark frequency is still above the peak of the circuit l2 characteristic in Fig. 2)

and that of resonant circuit 25 will decrease.

Underthese conditions, leg A of the cathoderay tube display 9X will lengthen, and leg B will shorten. This will indicate incorrect tuning.

If the mean ofthereceived mark and space frequencies shifts above the frequency Y, the

sirable, and in fact necessary, to'have the crossover frequency .Y' accuratelycentered between" the received mark-space frequencies. It is necessary to maintain this accuracy of tuning to preserve the proper keyingbias. .Sincelthe radiov frequency signal .is heterodyned down to pass through the mark/space filters,the beating oscilflator used for tuning must'be set to exactly center .the'mark and space frequencies about the crossover at'Y. 'In high-speed telegraphy, this'tuning 'isvery' diflicultto achieve without a visual indicator of the type-disclosed. 'When the frequency Y is accurately centered between the received markspace frequencies, signals having rather large ranges of frequency shift may be received properly.

;-fr' o i Fig; QZQfthatf the i376 ince by the circuit of this invention, tuning is ans-an indicatedby the; symmetry 1 orgnonsymmetry of the X, or in other wordsjby; :thglength otone leg relative to that of theother leg the' absolute. lengths of the-legs havenothing to do withthe.

The connections to theI cathode :rayltube l 4,1 for producing the electron beam including. the) iocus.

and intensity controls} are illustrated in -Fig, 1

but are not described indetail herein since this is a more or less conventional arrangement.-

l illustratesithe application of this invention to a singleFS receiver. Thetuning indicator of this invention may be appliedto a threes-setv diversity receiverused forFs telegraphy Fig. 3 illustrates a circuit of the latter type.

The terminals labeled Mi, M2, M3 are. fed from; the three mark filters of. athree-set diversity receiver for PS signals=,; such as disclosed, for. ex: ample, in my said copendingapplication. The terminals labeled S l S2, S3 yare fedfrom the three space filters of such receiver. a Each Of these terminalsis connected to;,t he.anode.of a separate diode. Il'lStEifidOffilSllflg six, separate ,diodes as indicated, three twin diodes, for example. of the GAL5 type, may be used here, Thepathodes of the three mark diodes are paralleled and connected through couplingcondenser;29 tothe con trol grid 36, of the. first hali-3 lfOf afirst twinutriode, forexample of the IZAXZ type; Theca-thodes of the three space diodes areparalleled. and connected through coupling condenser 32 .-:to the control grid 33; ofthe firsthali ti ia second twin triode, for example-.ofthe lZAX'Ztype In the diversity receiverof my said application, diversity switching takes place, by means of gate tubes, prior to, thethree mark. filters v and the three, space; filters referred: toin the preceding, paragraph. However,- the tuning indicatorof this invention must be ableto operate .immanypneof the markfilter outputsand irom any ,onegof, the space filter outputs. The diode circuit just. (18-. scribed a lows a y of tham rkfiher.ou ut to be applied to tubeil; withoutgthenecessity-of directly paralleling thethree mark filter outputs.

Itisnot allowableto parallel the threemarkfilter outputs directly, ,in order to Iced ai'sir gle tube. The diode circuit, in. effect,v prevents one mark filter output from feeding into the other two mark filter outputs. Similarly, any of the space filter outputs may be applied. to tube .341 without the necessity of directly paralleling. thethree space filter outputs. The diode circuit'ldescribed pree vents one space filter output from feeding into the other two space filter outputs. In other words, the six diodes are supplied in orderthat the three mark filters and threevaspace filters may operate into the commonamplifier inputcircuits without interactionwln eiiect this gives a practical switching device which allows the strongest signal to override the weaker ones, by biasing diode action. A positive cutofi bias, here shown as 0.8 volt, is supplied to the diode cathodes to aid the switching action.

The first half 3| of the first twin triode supplies a rather large signal to the grid 35 of the second hali;-3.'6of..this" triode Shi .limitingisprovided in thisiprooe'ss. Similarly..t egfirst half. 341. of the second ,twin triode supplies; a rather... large signal tothegrid 3 I. of the, second halt :3 Biol this triode.

Some limiting. issalso. provided in.this process. This, limiting serves .to keep theamplituda of the cathode ay. display. at a, more. constant. value in the presence of. additions and ,subtractions of the various signals as passed by.'-the. cathodesof, the mark and space .diode's. Such additionsor subtractions may beproducedJdueto theiact that, occasionally, jthe. signals areequallypassed. by

twoor three receivers Thephasarelations oi the sever-alfsignalsmay, occasionally Joe. such as, to

give. substractionslof. the various; signals-u This.

limiting would not begnecessaryifon operation withs a single receiver The; mark esonant circuit lzfis, in the. anode circuitLof the second-half 360i the. first .twin. triode. The space resonant circuit 2 5,. is in, the anode-circuit of. the; second .halilts .of thjesecond.

twin :triode. The connections ,to .the. cathode ray.

tube ll are thesame asin Fig..,1.

The. circuit of Fig, 3 operates in the. same mane her as that of Fig.1, to .producean ffX onthe face of the oathoderay tube. Thadescription. of operation will therefore nqt-berepeated. The symmetry or non-symmetry of. the..cathode:ray tubefsf X isan indication ofwithe tuningi What Iclaim to be my inventionds 1. Atuning indicatonfora frequency shift tele graphy receiver adapted tp receive alternatively present signals of one frequencyf representing mark, a d na Qt another i au n i" r r ati 593%; c m ris a 1$ ?1 1 8349 for a in si na pf maree u ncy; a d a t nss sn 0 s q i e uencn se eud: s e iv means for passingsignals oispacefirequeney andatte atin s n imarhz eeue c imean f app ying; si n s o a k; r u n r id. fi s selective means, means for applying signals'of space frequency to said second selective; means. a cathode ray, tube having means for "producing an electron beam,. defiecti,n 2 means .operative n said beam, and receptive 50f. the: :output; :of said first selective: means, i or; deflecting. said ;beam 1 in one sense. inaccordance withzthe outputgof vsaid first. selective means; anddeflecting; meansoperative .on: said beam, and receptive of the output :of said second selectivemeans, for'deflecting said beam ina difierent sensein'iaccordanceiwith the output ofisaid second.selective-means:

.2. A tuning indicator inaccordancewithclaim 1,:wherein said mark=frequencyi applying means includesa filter .for passing saidimark frequency and an amplifier.

3'. A tuning. indicatorin accordance with claim 1, wherein said firstl selective-means. comprises a' resonant circuit, and= wherein said markiirequency applying means. includes aifilter .iorxpa'ssing said markfrequency amplifier 4. Atuning indicator in accordance .with' claim 1, wherein said first and second selective means each comprises a resonant circuiu. wherein said marklfrequency applying means includes a filter for :passing; said mark frequency and 1 an. amplifier; and wherein said space ir'equency applying means includes a-filter :for passing-said space frequency and an. amplifier.

59A tuning: indicator for frequency shiit telegraphy receiverv adapted to receive. alternatively-present signals of one frequency representing mark and signals of another frequency representing space, comprising first selective means for passing signals of mark frequency and at,-

tenuating signals of space frequency, second se-. lective means for-passing signals of spacetfre quency and attenuating signals of 'mark fre quency means for applying signals" of mark frequency to said first selective. means,- means for applying signals of space frequency to said second selective means, a cathode ray tube having cordance with the output of said first selective means, and deflecting means operativeon "said beam, and receptive of the output of said-second selective means, for deflectingsaid beam linearly in another direction in accordance with the output of said second selective-means; I

6. A tuning indicator for a frequency shift telegraphy receiveradapted to receive alternatively-present signals of one frequency representing mark and signals of another frequency representing space, comprising first selective means for passing signals of mark frequency and attenuating signals of space frequency, second selective means for passing signals of space frequency and attenuating signals of mark frequency, means for applying, signals of mark frequency to said first selective means, means for applying signals of space frequency to said second selective means, a cathode ray tube having means for producing an electron beam, deflecting means operative on said beam, and receptive of the output of said first selective means, for defleeting said beam linearly in one direction in accordance with the output of said first selective means, and deflecting means operative on said beam, and receptive of the output of said second selective means, for deflecting said beam linearly in another direction in accordance with the output of said second selective means, said other direction making an acute angle with said one direction. V I a v 7. A tuning indicator for ;a frequency shift telegraphy'receiver adapted" to receive alternatively-present signals of one frequency representing mark and signals of another frequency representing space, comprising firstselective means for passing signals of mark frequency and attenuating signals of space frequency, second selective means for passing signals of space frequency and attenuating signals of mark frequency, means for applying signals of mark fre: quency to said first selective means, means for applying signals of space frequency to said second selective means, a cathode ,ray tube having means for producing an electron beam and having a plurality of deflecting electrodes, means connecting the output of said first selective means to one combination of electrodes to produce defiection of said beam in one sense, and means connecting the output of said second selective means to a different. combination of electrodes to produce deflection of said beam in another sense.

. 28. A tuning, indicator for a frequency shift *telegraphy receiver adapted to receive alternatively-present signals of one frequency representing mark and signals of another frequency representing space, comprising first selective means for passing signals of mark frequency and attenuating signals of space frequencmsecond selective means for passing signals of space frequency and attenuating signals of mark frequency, means'for applying signals of mark frequency to said first selective means, means for applying signals of space frequency to said second selective means, a cathode ray tube having means for pro-' ducing an electron beam and having four orthogonally-related deflecting electrodes, means connecting the-outputof'said first selective means to two electrodes in space quadrature to produce linear deflection 'of said beam in one direction. and means connecting the output of said second selectivemeans to two other electrodesv in space quadrature to produce'flinear deflection of said beam in another direction.

'9. A tuning indicator for a frequency shift telegraphy.receiveradapted to receive alternatively-present signals of one frequency representing mark and signals of another frequency representing space, comprising first selective means for passing signals of mark frequency and attenuating signals of space frequency, second selective means for passing signals of space frequency and attenuating signals of mark frequency,f means for applying signals of mark frequency tosaid first selective means, means for'applying signals of space frequency to said second selective means, a cathode ray tube having means for producing an electron beam and having four orthogonally-related deflecting electrodes, means for applying the entire voltage output of said first selective meansto one electrode and only a portion of such voltage to another electrode in space quadrature relation to said one electrode, thereby to produce linear deflection of said beam in one direction, and means for applying the entirevoltage output of said second selective means to still another electrode and only a portionof such voltage to an electrode in space quadrature relation to said'last-mentioned electrode, thereby to produce linear deflection of said beamin another direction. 7

'10. A tuning indicator as defined in claim 9, wherein'said'one electrode and said last-mentioned electrode are oppositely disposed with respect to'the electron beam.

' 11. A tuning indicator as defined in claim 9, wherein said one electrode and said last-mentioned electrode are oppositely disposed with respect to the electron beam, and wherein the portions of the voltage outputs of the first and sec- 1 0nd selective means are applied to the same electrode. a v

' 12-. A tuning indicator in accordance with claim 9, wherein said mark frequency applying means includes a filter for passingsaid mark frequency .1 and an amplifier, and wherein said space fre- Number.

quency'applying means includes a filter for passing'said space-frequency and an amplifier.

1 4 BERTRAM A. TREVOR.

I REFERENCES CITED he following references are of record in the flle of this patent:

.UNITED STATES PATENTS Name Date 2,233,751 Seeley' Mar. 4, 1944 2,477,963 Chapin Aug. 2, 1949 j 1 FOREIGN PATENTS Number Country Date 891,937 France Mar. 23, 1944 

